1. Field of the Invention
The invention disclosed herein relates to radioactive implants for medical therapeutic purposes, referred to in the art as "radioactive seeds," "seeds," or "sources." The invention relates to seeds for therapeutic radiation treatment of oncological and other medical conditions. More particularly, the invention is directed to a novel radioactive seed for interstitial implantation brachytherapy and also for general brachytherapy treatments. The invention is also directed to methods of making the seeds and methods of using the seeds.
2. Background of the Invention
The localized treatment of tumors and other medical conditions by the interstitial implantation of radioactive materials is a recognized treatment modality of long standing. Radioactive implants are used to provide radiation therapy in order to reduce or prevent the growth of tumors that cannot be removed by surgical means. Radioactive implants are also used to prevent the growth of microscopic metastatic deposits in lymph nodes that drain the region where a tumor has been removed. Implants are also used to irradiate the postoperative tumor bed after the tumor is excised. Implantation of radioactive sources directly into solid tumors for the destruction of the tumors is used in a therapy referred to as brachytherapy.
Brachytherapy is also used to prevent the regrowth of tissue in circumstances such as the treatment of arteries for occlusive disease. Brachytherapy is applied, for example, in the treatment of atherosclerosis to inhibit restenosis of blood vessels after balloon-angioplasty or other treatments to open occluded or narrowed vessels. These brachytherapy treatments involve a short-term application of extremely radioactive sources. The applications can be for periods as short as a few minutes. This form of brachytherapy may therefore be contrasted with the treatment of tumors where lower activity sources are used for longer periods of time that may be measured in hours or days or may involve permanent implantation.
Treatment of medical conditions with the local application of radiation by implantation concentrates the treatment on the adjacent tissue and advantageously minimizes the exposure of more distant tissues that it is not desired to irradiate. Direct implantation of radioactive sources into tumors often permits the application of larger doses of radiation than may otherwise be achieved because the radiation is applied directly at the site to be irradiated. Local application of brachytherapy to non-cancerous conditions also allows the use of more intensive treatment than is possible by other means.
In the prior art, brachytherapy "sources" are generally implanted for short periods of time and usually are sources of high radiation intensity. For example, irradiation of body cavities such as the uterus has been achieved by placing radium-226 capsules or cesium-137 capsules in the lumen of the organ. In another example, tumors have been treated by the surgical insertion of radium needles or iridium-192 ribbons into the body of the tumor. In yet other instances gold-198 or radon-222 have been used as radioactive sources. These isotopes require careful handling because they emit highly energetic and penetrating radiation that can cause significant exposure to medical personnel and to the normal tissues of the patient undergoing therapy. Therapy with sources of this type requires that hospitals build shielded rooms, provide medical personnel with appropriate protection and establish protocols to manage the radiation hazards.
The prior art interstitial brachytherapy treatment using needles or ribbons has features that inevitably irradiate normal tissues. For example, normal tissue surrounding the tumor is irradiated when a high energy isotope is used even though the radiation dose falls as the square of the distance from the source. Brachytherapy with devices that utilize radium-226, cesium-137 or iridium-192 is hazardous to both the patient and the medical personnel involved because of the high energy of the radioactive emissions. The implanted radioactive objects can only be left in place temporarily; thus the patient must undergo both an implantation and removal procedure. Medical personnel are thus twice exposed to a radiation hazard.
In prior art brachytherapy that uses long-term or permanent implantation, the radioactive device is usually referred to as a "seed." Where the radiation seed is implanted directly into the diseased tissue, this form of therapy is referred to as interstitial brachytherapy. It may be distinguished from intracavitary therapy, where the radiation seed or source is arranged in a suitable applicator to irradiate the walls of a body cavity from the lumen.
Migration of the device away from the site of implantation is a problem sometimes encountered with presently available iodine-125 and palladium-103 permanently implanted brachytherapy devices because no means of affirmatively localizing the device may be available.
The prior art discloses iodine seeds that can be temporarily or permanently implanted. The iodine seeds disclosed in the prior art consist of the radionuclide adsorbed onto a carrier that is enclosed within a welded metal tube. Seeds of this type are relatively small and usually a large number of them are implanted in the human body to achieve a therapeutic effect. Individual seeds of this kind described in the prior art also intrinsically produce an inhomogeneous radiation field due to the form of the construction.
The prior art also discloses sources constructed by enclosing iridium metal in plastic tubing. These sources are then temporarily implanted into accessible tissues for time periods of hours or days. These sources must be removed and, as a consequence, their application is limited to readily accessible body sites.
Prior art seeds typically are formed in a manner that differs from isotope to isotope. The form of the prior art seeds is thus tailored to the particular characteristics of the isotope to be used. Therefore, a particular type of prior art seed provides radiation only in the narrow range of energies available from the particular isotope used.
Brachytherapy seed sources are disclosed in for example, U.S. Pat. No. 5,405,165 to Carden, U.S. Pat. No. 5,354,257 to Roubin, U.S. Pat. No. 5,342,283 to Good, U.S. Pat. No. 4,891,165 to Suthanthiran, U.S. Pat. No. 4,702,228 to Russell et al, U.S. Pat. No. 4,323,055 to Kubiatowicz and U.S. Pat. No. 3,351,049 to Lawrence, the disclosures of which are incorporated herein by reference.
The brachytherapy seed source disclosed in U.S. Pat. No. 5,405,165 comprises small cylinders or pellets on which palladium-103 compounded with non-radioactive palladium has been applied by electroplating. Addition of palladium to palladium-103 permits electroplating to be achieved and allows adjustment of the total activity of the resulting seed. The pellets are placed inside a titanium tube, both ends of which are sealed. The disclosed invention does not provide means to fix the seed source within the tissues of the patient to ensure that the radiation is correctly delivered. The design of the seed source is such that the source produces an asymmetrical radiation field due to the radioactive material being located only on the pellets. The patent also discloses the use of end caps to seal the tube and the presence of a radiographically detectable marker inside the tube between the pellets.
U.S. Pat. No. 5,354,257 relates to radioactive iridium metal brachytherapy devices positioned at the end of minimally invasive intravascular medical devices for providing radiation treatment in a body cavity. Flexible elongated members are disclosed that can be inserted through catheters to reach sites where radiation treatment is desired to be applied that can be reached via vessels of the body.
U.S. Pat. No. 5,342,238 discloses methods such as sputtering for applying radioactive metals to solid manufactured elements such as microspheres, wires and ribbons. The disclosed methods are also disclosed to apply protective layers and identification layers. Also disclosed are the resulting solid, multilayered, seamless elements that can be implanted individually or combined in intracavitary application devices.
U.S. Pat. No. 4,891,165 to Suthanthiran relates to the production of brachytherapy seed sources and discloses a technique for use in the production of such sources. The patent discloses an encapsulation technique employing two or more interfitting sleeves with closed bottom portions. The open end portion of one sleeve is designed to accept the open end portion of a second slightly-smaller-diameter sleeve. The patent discloses the formation of a sealed source by sliding two sleeves together. Seeds formed by the Suthanthiran process may have a more uniform radiation field than the seed disclosed by U.S. Pat. No. 5,405,165. However, the seed disclosed by Suthanthiran provides no means for securely locating the seed in the tissue of the patient. The U.S. Pat. No. 4,702,228 to Russell et al. relates to the production of brachytherapy seed sources produced by the transmutation of isotopically enriched palladium-102 to palladium-103 by neutrons produced by a nuclear reactor. The Russell patent also discloses a titanium seed with sealed ends, similar to that of Carden, containing a multiplicity of components. A seed produced in this manner is associated with yielding a less than isotropic radiation field.
U.S. Pat. No. 4,323,055 teaches a titanium seed with ends sealed by laser, electron beam or tungsten inert gas welding. The radioactive component of the seed is disclosed to be a silver bar onto which the radioisotope iodine-125 is chemisorbed. Seeds produced in this manner also tend to produce an asymmetric radiation field and provide no means of attachment to the site of application in the patient.
U.S. Pat. No. 3,351,049 discloses a radioactive seed with a titanium or plastic shell with sealed ends. Seeds are disclosed containing a variety of cylindrical or pellet components onto which one of the radioisotopes iodine-125, palladium-103, iridium-192 or cesium-131 is incorporated. The structure of the disclosed seeds yields a non-homogeneous radiation field and provides no means for accurately positioning the seed in the tissue that it is desired to irradiate.
Currently available brachytherapy seeds do not easily lend themselves to association with suture material. For example, iodine-125 seeds currently in use are placed inside suture material at the time of manufacture. However, the insertion process is tedious and time consuming and has the potential for significant radiation exposure to the production personnel involved. Additionally, because of the natural decay of the radioisotope, the suture material thus produced has a short shelf life. As a second example, the manufacturing process used to produce the palladium-103 seeds that are currently in use results in end-roughness of the encapsulation of the seed. The capsules are not placed inside suture material because the end-roughness makes insertion very difficult. Rigid rods are produced in present technology by the insertion of seeds into suture material followed by heat treatment to form a rigid rod containing the seed. These rods are difficult to produce, very fragile and sensitive to moisture. The presently available brachytherapy technology requires that most physicians use suture material preassembled with the seeds already inside. Similarly, rigid materials used by surgeons for brachytherapy are pre-manufactured and purchased readymade.